Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/20—Measuring; Control or regulation
  • B01F35/21—Measuring
  • B01F35/211—Measuring of the operational parameters
  • B01F35/2115—Temperature
  • B01F35/21151—Temperature using infrared radiation thermometer or pyrometer or infrared sensors for temperature measurement without contact
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/20—Measuring; Control or regulation
  • B01F35/22—Control or regulation
  • B01F35/221—Control or regulation of operational parameters, e.g. level of material in the mixer, temperature or pressure
  • B01F35/2214—Speed during the operation
  • B01F35/22142—Speed of the mixing device during the operation
  • B01F35/221421—Linear speed of the tip of a moving stirrer during the operation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/20—Measuring; Control or regulation
  • B01F35/22—Control or regulation
  • B01F35/221—Control or regulation of operational parameters, e.g. level of material in the mixer, temperature or pressure
  • B01F35/2216—Time, i.e. duration, of at least one parameter during the operation
  • B01F35/22161—Time, i.e. duration, of at least one parameter during the operation duration of the mixing process or parts of it
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B13/00—Conditioning or physical treatment of the material to be shaped
  • B29B13/02—Conditioning or physical treatment of the material to be shaped by heating
  • B29B13/021—Heat treatment of powders
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B7/00—Mixing; Kneading
  • B29B7/002—Methods
  • B29B7/005—Methods for mixing in batches
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B7/00—Mixing; Kneading
  • B29B7/02—Mixing; Kneading non-continuous, with mechanical mixing or kneading devices, i.e. batch type
  • B29B7/06—Mixing; Kneading non-continuous, with mechanical mixing or kneading devices, i.e. batch type with movable mixing or kneading devices
  • B29B7/10—Mixing; Kneading non-continuous, with mechanical mixing or kneading devices, i.e. batch type with movable mixing or kneading devices rotary
  • B29B7/12—Mixing; Kneading non-continuous, with mechanical mixing or kneading devices, i.e. batch type with movable mixing or kneading devices rotary with single shaft
  • B29B7/16—Mixing; Kneading non-continuous, with mechanical mixing or kneading devices, i.e. batch type with movable mixing or kneading devices rotary with single shaft with paddles or arms
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B7/00—Mixing; Kneading
  • B29B7/80—Component parts, details or accessories; Auxiliary operations
  • B29B7/82—Heating or cooling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/022—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the choice of material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
  • B29C48/475—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die using pistons, accumulators or press rams
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C67/00—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00
  • B29C67/24—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00 characterised by the choice of material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
  • B29C43/02—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles
  • B29C43/16—Forging
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/001—Combinations of extrusion moulding with other shaping operations
  • B29C48/0011—Combinations of extrusion moulding with other shaping operations combined with compression moulding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
  • B29C48/04—Particle-shaped
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
  • B29C48/07—Flat, e.g. panels
  • B29C48/08—Flat, e.g. panels flexible, e.g. films
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2027/00—Use of polyvinylhalogenides or derivatives thereof as moulding material
  • B29K2027/12—Use of polyvinylhalogenides or derivatives thereof as moulding material containing fluorine
  • B29K2027/18—PTFE, i.e. polytetrafluorethene, e.g. ePTFE, i.e. expanded polytetrafluorethene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
  • B29K2105/0005—Condition, form or state of moulded material or of the material to be shaped containing compounding ingredients
  • B29K2105/0032—Pigments, colouring agents or opacifiyng agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
  • B29K2105/25—Solid
  • B29K2105/251—Particles, powder or granules
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
  • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
  • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08J2327/18—Homopolymers or copolymers of tetrafluoroethylene

Definitions

• This invention relates to polytetrafluoroethylene (PTFE). More specifically, the invention relates to the production of articles made from PTFE in shorter times and by simpler methods than has been previously possible.
• PTFE has many commercial uses. PTFE has a useful temperature range from -200°C or lower, up to a maximum of 260°C. Production of articles is expensive as it has not been possible to use conventional plastic processing techniques. At the present time powder metallurgy processing techniques such as those used with metal alloys and ceramics are applied to PTFE to produce molded products. In one embodiment PTFE granules are molded at pressures in the range of 13.8 to 68.9 megapascals followed by sintering at temperatures of about 380°C. PTFE products can be ram extruded at slow rates, but a processing aid, generally naphtha must be used and it is then necessary to remove this processing aid by heating after the molding step.
• PTFE resins which are commercially available may be directly formed into articles of a desired shape by initially carrying out a high intensity mixing and heating process wherein the resin is intensively mixed and thermokinetically heated in a manner which controls thermal degradation and without shearing action occurring.
• One type of high intensity mixer is shown by Goeser et al in U.S. patent 3,266,738, published August 16, 1966. This patent describes a high intensity mixer available on the market today, under the trade mark Gelimat, made by Draiswerke GmbH.
• the mixer includes a plurality of blades which rotate about an axis within an enclosed container. In the past tip speeds have been in the order of up to 25 meters per second. Higher tip speeds have not generally been feasible because of problems controlling the temperature of the batch at the discharge.
• PTFE resins may be first processed in a high intensity mixer having blade tip speeds of at least 30 meters/second and preferably 40 meters/second or higher. In this process the resin is intensively mixed and thermokinetically heated to the desired forming temperature which is above 370°C and preferably 450°C or higher. To reach this temperature range the mixing step requires a period of time in the order of 1 - 2 minutes.
• the heated unstabilized resin After the heated unstabilized resin is discharged from the high intensity mixer it must be processed or formed into an article before the material cools. In the form it exits from the high intensity mixer it may be processed directly by some conventional or modified plastic fabrication techniques, such as compression molding, transfer molding, forging, stamping, ram extrusion or pressing into the desired shape and thickness.
• Fabricated articles produced by the process of the present invention have physical properties at least as good as those articles produced by conventional methods.
• the present invention provides, a process for production of a shaped polytetrafluoroethylene article comprising, introducing polytetrafluoroethylene granules into a high intensity mixer comprising an enclosed container having a plurality of blades rotatable on arms about a central axis; rotating said blades at a blade tip speed of at least 30 meters per second whereby the polytetrafluoroethylene granules are subjected to an intense mixing and thermokinetic heating action of the rotating blades until the granules become heated to a predetermined discharge temperature of above 370°C; discharging the polytetrafluoroethylene granules at said discharge temperature; forming the discharged, heated, granules into an article of desired shape at or below said discharge temperature; and cooling the shaped article.
• the blade tip speed is at least about 40 meters/second and the predetermined discharge temperature is at least about 450°C. With a blade tip speed of about 35 meters/second and a discharge temperature of about 450°C the mixing and heating step is in the range of about 80 - 120 seconds. When the blade tip speed is about 40 meters/second and the discharge temperature in the range of about 475 - 480°C the mixing and heating step is in the range of about 60 - 80 seconds.
• the article comprises a sheet of polytetrafluoroethylene and the forming step comprises pressing the discharged resin between platens to form the sheet.
• the pressing occurs between hot plates at a temperature of at least about 150°C and a pressure of at least about 2200 kilopascals, the pressing step lasts for about 3 minutes, followed by a cooling step for about 2 minutes.
• the total processing time for making the article is in the range of about 6 - 7 minutes.
• PTFE resin generally in granular form, may be processed without additives, or may include additives for stabilization. Additives such as pigments may be added for colour as desired.
• the forming may take place in a press and in one embodiment is a coating layer on a substrate.
• the desired shape is a billet which is cooled to a temperature suitable for forming into a finished article by direct stamping or forging.
• the resin is preferably discharged from the intensive mixing step directly into a compression molding step.
• the forming comprises extruding the discharged resin in a ram extruder.
• the article formed into a desired shape is preferably held at an elevated temperature above a predetermined forming temperature, i.e. at least 150°C or in some cases at least 170°C, prior to cooling the shaped article.
• High intensity mixers are known for processing thermo-plastic and thermo-setting materials.
• Ultra high molecular weight polyethylene articles may be processed in a high intensity mixer, as disclosed in U.S. patent 4,272,474.
• the Gelimat one example of a high intensity mixer, is satisfactory for operating the present process.
• Such a mixer has a plurality of blades attached at the end of arms radiating from a central axial shaft which rotates within an enclosed container. Variation in the speed of the rotating shaft changes the blade tip speed and in the present invention it is found that blade tip speeds of 30 meters/second and higher are satisfactory.
• the Gelimat high intensity mixer may be of the screw feed design having a feed screw at one end which feeds resin into the mixer, or may be of the stop-start type which includes an input hatch at the top of the container, which is opened to feed material into the mixer. In both cases, in order to empty the mixer there is an exit flap which opens to permit the batch of material processed in the mixer to be dropped out and removed for further processing.
• the mixer is preferably fitted with a system for monitoring the infrared radiation from the batch and hence temperature of the batch in the mixer separately from the temperature of the mixer walls and blades.
• the batch is discharged from the mixer when the batch temperature reaches a predetermined level.
• the measurement of the temperature of the batch by infrared radiation is instantaneous and is quite unrelated to the temperature of the mixer walls or blades.
• the exit flap of the mixer opens and the batch is discharged for further processing.
• the energy from the high speed rotating blades in the mixer body intensively mix and thermokinetically heat the PTFE resin batch.
• the control of the mixing and heating step is by temperature, it is found that the time of each batch can vary slightly due to a number of reasons, however, the state of each batch and its discharge temperature are constant.
• batches of PTFE resin ranging from 200 - 300 grams were processed in a Gelimat high intensity mixer having a capacity of 1.4 litres.
• the temperature of each batch was measured using an infrared monitoring system which determined the infrared radiation of the resin in the mixer through an optical fiber system. The system was capable of accurate temperature measurement in the range from 160 - 600°C.
• the temperature of the batch discharging from the mixer was also measured with a pocket probe digital pyrometer fitted with a needle-nose probe.
• the time in seconds from introduction of the resin to the mixer until discharge, was measured with a stopwatch. Tests were carried out with the mixer having blade tip speeds of approximately 35 meters/second and 40.5 meters/second.
• the batches of PTFE hot resin discharging from the Gelimat high intensity mixer were immediately pressed into sheets having a thickness of approximately 3 mm.
• the press plates were steam heated to temperatures of 170°C with the frame preheated to temperatures of up to 200°C to avoid too great a thermal quenching effect.
• the temperature of the PTFE batch in the press was below the discharge temperature from the mixer.
• Pressures in the press were as low as 2200 kilopascals.
• the pressing cycle lasted for approximately 3 minutes at the raised temperature, followed by an approximately 2 minute cooling phase, during which time water was circulated through the press to cool the plates.
• the limitations on the press were limitations of existing equipment, larger sheets and articles could be more easily formed in presses or molds heated to temperatures closer to the discharge temperature of the resin.
• the properties of the pressed sheets from PTFE were tested by standard measurement techniques. The specific gravity was measured by water displacement, hardness tests and tests for dielectric response were carried out, and a differential scanning calorimeter (DSC) was used for determining melting points at both heating and cooling rates of 20°C per minute. In the DSC tests, after the first heating cycle, the sample was maintained above the melting point for approximately 5 minutes before the cooling cycle commenced and then held at approximately 45°C for 5 - 10 minutes before the second heating cycle was begun.
• DSC differential scanning calorimeter
• Table II sets out the results of the physical property analysis.
• the measurement of the melting points was carried out on a Perkin Elmer Model 2C differential scanning calorimeter, the readings are taken from the second heating cycle.
• the melting points increased from the first heating cycle to the second heating cycle by 1° and 2.2°C for the first and second tests respectively.
• the melting point for the second heating cycle decreased by approximately 0.5°C. This would indicate that the mixing and heating step causes the PTFE resin to pass through an effective melt stage so that the crystalline state of the processed resin is closer to the equilibrium condition of the material.
• the physical properties of the PTFE articles produced by the process of the present invention are as good if not better than sheets of PTFE produced by conventional methods.
• the PTFE resin discharged from the mixer is formed into a billet which is cooled to a temperature suitable for forming into a finished article by direct stamping or forging.
• the resin is discharged from the mixer directly into a compression molding step. The forming may also occur in a ram extruder.
• PTFE applications include coatings on a substrate. This application is particularly useful because of the chemical resistance properties and heat properties of PTFE.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Manufacturing & Machinery (AREA)
• Health & Medical Sciences (AREA)
• Materials Engineering (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)

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• 1982
  • 1982-04-19 US US06/369,584 patent/US4420449A/en not_active Expired - Lifetime
• 1983
  • 1983-08-23 EP EP83304863A patent/EP0134342B1/de not_active Expired

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